Project Summary Great strides have been made in controlling pain during surgery, however postoperative pain remains poorly controlled and undermanaged, with upwards of 50% of patients reporting significant persistent postoperative pain. Although the mechanisms of postoperative pain are still incompletely understood, research has shed light on one potentially important immune cell. Mast cells play a crucial role in the body's innate immune response to pathogens and are capable of acting locally at the site of injury. These bone marrow derived immune cells can be found in close proximity to peripheral nerve endings where upon activation they can release a broad range of pro-inflammatory cytokines and mediators. The role of mast cells in mediating postoperative pain is incompletely understood, although studies using the mast cell stabilizer cromoglycate demonstrate that this immune cell is pivotally involved in contributing to nociception in animal models of postoperative pain. Thus, there is a compelling need for fundamental research aimed at understanding the mechanisms of postoperative pain and in identifying potentially novel therapeutic approaches for treating it, as typically used analgesics offer patients either incomplete efficacy or are limited by substantial adverse effects. Towards this objective, our lab has previously published data identifying a novel mast cell specific receptor, Mas-related G-protein-coupled receptor B2 (MRGB2) and its human orthologue, MRGX2, in non-allergenic activation of mast cells. Our recent preliminary data have identified MRGB2 in mediating thermal and mechanical hypersensitivity post inflammation. Therefore, we propose to test the central hypothesis that postoperative tissue injury leads to activation of mast cells via MRGB2 and contributes to the development of mechanical and thermal allodynia. The following specific aims will test this innovative hypothesis: Specific Aim 1 Characterize the contribution of mast cells and their receptor MRGB2 to incision induced allodynia in a mouse model of postoperative pain Specific Aim 2 Identify the mechanisms by which mast cell receptor MRGB2 contributes to postoperative pain Specific Aim 3 Examine the interaction between mast cells and peripheral sensory neurons in a mouse model of postoperative pain using in vivo live imaging